The benefits of collecting medical information from a person over a long time period and during everyday life have long been prophesised. In recent years, many research groups have been investigating body sensor networks (BSNs). These are networks of multiple sensors or sensing devices or sensing nodes, deployed around, and even in, the body and transmitting their data over a digital radio link. Thus, each sensor should be as discrete and small as possible.
A number of protocols are currently known which purport to be protocols for ‘low-power’ networks and might therefore be suitable for BSNs. Examples of such protocols are described in “Part 15.4: Wireless Medium Access Control (MAC) and Physical Layer (PHY) Specifications for Low-Rate Wireless Personal Area Networks (LR-WPANs)”, IEEE Std 802.15.4-2006, and Wei Ye et al. “S-MAC: An Energy-Efficient MAC Protocol for Wireless Sensor Networks”. However, the design of these networks may not be optimal very low power devices, especially if the majority of devices on the network are just collecting data from sensors and are forwarding these readings to a single device.
A BSN, by its very nature, is a mobile network and can be worn on the body, for example. Additionally, an access device or ‘collating’ device is provided, which collects data from the sensor nodes and which may also be worn on the body. However, it would be advantageous if this portable device could be taken off in certain areas, e.g., while the person wearing the BSN is at home. Also, in order to reduce battery usage of the portable device it would be an advantage if fixed, e.g. mains powered, devices could take over the network.